Amine oxide surfactants are widely used in commercial cleaning compositions. When formulated into detergents for use in automatic dishwashing they are very effective for grease removal and reduction of filming and spotting on dishware and tableware. These surfactants are produced by oxidation of tertiary amines, the oxidation is carried out in liquid media, therefore if the amine oxide is to be used in solid compositions an after-treatment step, such as spray-drying or evaporation, would be required, increasing the capital cost and the energy requirements of the production process.
Detergency bleach is part of most of the dishwashing products. Bleach species can interact with amine oxide in the dishwashing product, this interaction no only decreases the amount of bleach and amine oxide available for the dishwashing process but also generates amine species given rise to malodour problems.
The syntheses most commonly employed for the production of amine oxides is carried out in aqueous solution, as taught in for example U.S. Pat. No. 4,748,275 and U.S. Pat. No. 4,247,480. The resulting amine oxides are obtained in aqueous liquid, this is valuable for aqueous detergents, however, cannot be readily used in anhydrous liquid detergents. Processes for the preparation of amine oxides in organic solvents are also known in the art. U.S. Pat. No. 3,776,959 discloses a process for the production of amine oxides in non-polar solvents. U.S. Pat. No. 5,130,488 discloses a process for the production of amine oxides in an organic solvent. The organic solvent may be a solvent in which the amine oxide is soluble at the reaction temperature but insoluble at a lower temperature.
Unitised doses of dishwashing detergents, especially water-soluble pouches, capsules and sachets are very attractive to consumers. A challenge that the formulator is faced with when designing water-soluble detergents containing amine oxide surfactants, especially in liquid form, is that the amine oxide needs to be dissolved in a solvent suitable for the dishwashing process, compatible with the material of the water-soluble unit dose form and which will not impair the dissolution of the unit-dose detergent.